How Often Does Google Update its Calendar Feeds?

Google Calendar does not sync subscribed iCal (.ics) feeds in real time. According to their Calendar Help documentation, the refresh rate for external feeds can take up to 12 hours. Previously, this was listed as "every few hours" or "up to 8 hours," but Google has recently updated this to reflect a longer potential delay.

Note: It may take up to 8–12 hours for changes made in an ICS feed to appear in your Google Calendar.

This means any updates made to your external calendar feed (such as new bookings or changes) may not appear immediately and could take several hours to sync.